On Tue, Jun 09, 2015 at 05:29:52PM +0800, Peter Zijlstra wrote:
> On Tue, Jun 09, 2015 at 11:13:40AM +0800, Huang Rui wrote:
> > +static void delay_mwaitx(unsigned long __loops)
> > +{
> > + u32 end, now, delay, addr;
> > +
> > + delay = __loops;
> > + rdtsc_barrier();
> > + rdtscl(end);
> > + end += delay;
> > +
> > + while (1) {
> > + __monitorx(&addr, 0, 0);
> > + mwaitx(delay, true);
> > +
> > + rdtsc_barrier();
> > + rdtscl(now);
> > + if (end <= now)
> > + break;
> > + delay = end - now;
> > + }
>
> How about you think instead and do something like:
>
> rdtsc(start);
> rdtsc_barrier();
>
> for (;;) {
> delay = min(MWAIT_MAX_LOOPS, loops);
>
> __monitorx(&addr, 0, 0);
> mwaitx(delay, true);
>
> rdtsc_barrier();
> rdtsc(end);
> rdtsc_barrier();
>
> loops -= end - start;
> if (loops <= 0)
> break;
>
> start = end;
> }
>
It looks better, thanks. :)
> > +}
> > +
> > +/*
> > * Since we calibrate only once at boot, this
> > * function should be set once at boot and not changed
> > */
> > @@ -118,7 +145,12 @@ int read_current_timer(unsigned long *timer_val)
> >
> > void __delay(unsigned long loops)
> > {
> > - delay_fn(loops);
> > + if (loops > MWAITX_MAX_LOOPS ||
> > + !static_cpu_has_safe(X86_FEATURE_MWAITT) ||
> > + boot_option_delay != DELAY_MWAITX)
> > + delay_fn(loops);
> > + else
> > + delay_mwaitx(loops);
> > }
>
> Then you can do away with that fallback entirely.
OK, I will submit V3 to remove kernel parameter and with the change of
delay method.
Thanks,
Rui
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